He succeeded his father, Araphor, upon his death in 1589, at the age of 116.

In T.A.1601, the twelfth year of Argeleb's reign, many hobbits migrated from Bree so Argeleb granted them the land beyond the Baranduin to dwell in. These hobbits were joined in The Shire by Stoors from Dunland around 1630.[3] Prior to this, the area of the Shire had been unpopulated and regarded as the king's hunting ground.

In T.A.1636 the Great Plague devastated Gondor (the King, his children and the White Tree perished) and moved north to the lands of Argeleb's rule.[3] Although the Great Plague decreased in severity as it moved north, there was still much suffering throughout Eriador; most of the people of Cardolan perished (especially those living in Minhiriath) including Cardolan's last prince. The last prince was buried in the Barrow-downs, which was also about the time that evil-spirits started coming from Angmar to dwell in the Barrow-downs.[4]

After having ruled for eighty-one years, he was succeeded by his son, Arvegil, upon his death in 1670.[2]

Argeleb's name is Sindarin for "Silver King" from ar meaning "royal", and celeb (becoming lenited to geleb) meaning "silver". It is likely that Argeleb II was named after his great-grandfarther, Argeleb I